The above stated method is frequently used for welding or glueing together plastic articles, for instance a tube end in a sleeve, in order to realize an air- or liquid-tight connection as well as a connection with tensile and pressure strength. In such a weld obtained by means of heat it is very important to have the temperature at the right level in order to soften, melt or cure the plastic materials, and also to have the time duration to ensure that the heat supply has been long enough to establish an intimate connection.